In Recovery...

Well, it was released a year ago but I only just found out about it last week. The SQL CAT team published a whitepaper last year called Database Snapshot Performance Considerations under I/O-Intensive Workloads. For a variety of workloads and with different numbers of concurrent database snapshots, it covers:

How much time does it take to create a database snapshot?

Transaction and I/O patterns during database snapshot creation

Transaction throughput and response time with multiple database snapshots